1. Field of the Invention
The present invention relates to an optical disc drive, and in particular, to a device and method for automatically controlling a sled loop gain for determining a driving voltage level of a sled motor.
2. Description of the Related Art
An optical disc drive for use in a digital video disc (hereinafter referred to as DVD) player or a compact disc (CD) player performs a focusing operation for shifting a lens up and down, and a tracking operation for shifting the lens to the left and right to settle the lens to direct a laser beam in an on-track position.
The tracking consists of two tracking steps. One is to drive a sled motor in order for a pickup to approach a target track, and another is to control a driving voltage provided to a tracking actuator to finely shift the tip of the lens to the target track. The former tracking step can shift the lens widely, but can not shift the lens promptly due to an inertia moment. The latter tracking step has a fast response, but has a narrow movable range of the pickup.
Accordingly, in order for the lens to jump over many tracks, the optical disc drive first shifts the lens by using the former tracking step, and then performs a fine tracking by using the latter tracking step. Furthermore, when the optical disc drive is driven in the state that the laser beam is on-track, the lens is finely tracked by the latter tracking step so as to shift to an outer circumference along the track on the optical disc. In order to compensate for the lean of the lens toward the outer circumference due to the fine tracking, the optical disc drive shifts the pickup by means of the former tracking step.
However, the conventional optical disc drive has a fixed sled loop gain for controlling the driving voltage supplied to the sled motor to compensate for the lean to be equal to a minimum driving voltage VsmvO for shifting the pickup. On the other hand, every product has a slightly different minimum driving voltage Vsmv0 for driving the pickup to shift over the track. Therefore, each product has low reliability.